Numerous prior art patents have attempted to solve the packaging pitch registration problems associated with metering a product to be packaged onto a web, sealing a second web to the first and thereby enveloping the product then singulating the packaged product. Brock 2,896,387; Smith 2,928,221; Lewi 2,896,943; and Mahaffy 4,034,536 add the additional essential steps of heating and thermoforming a pocket in one or both packaging webs to prevent product migration on the lower web as it is transported between the filling and sealing stations. Baumstingl 4,133,162 and Limmer 3,557,517 add the additional essential steps of introducing mold cavities which move with the packaging web through the filling, sealing and cut-off stations and means of deforming at least one of the packaging webs into the moving cavities in order to prevent product migration on the web between the filling and sealing stations.
Prior art devices such as shown by Brock, Smith and Lewi, supra, use apertured belts to support and transport in a straight line path semi-rigid plastic films which are thermally deformed to include five-sided depressions protruding through the apertures in the belt. In for instance the devices of Brock and Smith, the thermoformed depressions are sized so as to conform to and enter into positive driving engagement with the apertured belt. Lewi teaches the use of a system of hinged clamping elements arranged in the form of a belt to positively clamp and thereby drive the packaging webs through the thermoforming, filling, sealing, and cutting stations without requiring that the thermoformed depression enter into driving engagement with the apertured belt. In all three patents, product is introduced into the thermally deformed depressions and is prevented from migrating out of position by virtue of the sidewalls and depth of the depressions.
Mahaffy teaches the use of edge claps to support and drive in a straight line path a semi-rigid pair of packaging webs through thermoforming, filling, sealing, and punching stations in lieu of an apertured belt as in Brock. Like Brock, the product introduced to the thermally deformed depressions is prevented from migrating out of position by virtue of the sidewalls and depth of the depressions and further, in the types of products to be packaged as cited by Mahaffy, by the cohesion between these moist products and the packaging webs.
Baumstingl teaches the use of cooperating half molds carried on chains and arranged in a belt-like manner to define product enveloping cavities in a tubular packaging web and to advance these cavities in a straight line path through cross sealing and cross-cutting stations which act on the packaging web between mated half molds. Moreover, Baumstingl uses the mated half molds to prevent the product from migrating out of position between the filling and sealing stations.
Limmer allows for product enveloping, vacuum ported mold cavities to be carried on a drum in a circular path or on a belt in a straight line path. In both cases, a first flexible packaging web is drawn by vacuum into a cavity which both prevents product migration and defines the seal boundary between the two packaging webs.
The product in our application is relatively thin and flat and our application requires that the packaging web be extremely soft and pliable. Such supple webs cannot be thermoformed to act as reliable web driving means as taught by Brock and Smith. Nor can such thin and supple webs be thermoformed to provide depressions to precisely maintain thin products in position as they are transported in a straight line path between the filling and sealing stations as taught by Lewi and Mahaffy. The mold cavities introduced in the devices according to Baumstingl and Limmer could be used to package thin, flat products in soft and pliable webs, but the additional cost and complexity of the molds and means to make the web conform to the mold are rendered unnecessary by the device according to our invention which instead uses the web tension between the two packaging webs as they are drawn over and apertured support drum to maintain product placement much more accurately than any of the prior art devices as it is transferred between the filling and sealing stations. None of the devices using a straight line path between the filling and sealing stations can achieve a normal force between the two packaging webs and thereby hold the product in a precise position to the extent that our device achieves this end by wrapping the packaging webs over an apertured drum.